Add global media key remappings

Use the "Compose" key as a virtual modifier, then combined that with
F7-F12 to remap these key pairings as media keys with the same layout as
a Macbook Pro keyboard.

macOS.yaml

@@ -2,7 +2,19 @@
 # Wayland doesn't handle delay-less sequences properly, insert a delay.
 keypress_delay_ms: 20
 
+virtual_modifiers:
+  - Compose
+
 keymap:
+  - name: Global remaps
+    remap:
+      Compose-F7: PreviousSong
+      Compose-F8: PlayPause
+      Compose-F9: NextSong
+      Compose-F10: Mute
+      Compose-F11: VolumeDown
+      Compose-F12: VolumeUp
+
   - name: Terminal remaps
     application:
       only: